Modulator for microwave oscillations



April 1954 F. K. WILLENBROCK ETAL 77,

MODULATOR FOR MICROWAVE OSCILLATIONS 2 Sheets-Sheet 1 Filed Oct. 20, 1950 UTILIZATION cmcun l5 MICROWAVE GENERATOR 5 OLLECTOR F I6. I

MAGNETIC FIEL X-AXIS Z-AXIS OF CAVITY INVENTORS l9 FREDERICK KARL WILLENBROCK STUART P. COOKE BY M FIG. 2"A.

ATTORNEY April 27, 1 54 F. K. WILLENBROCK ET AL 2,677,107

MODULATOR FOR MICROWAVE OSCILLATIONS iled Oct. 20, 1950 2 Sheets-Sheet 2 Poul OJ Pin Pout P 16 I56 I6 16 I63 I62 Y mhos FIG. 5

2o 22 2o 22 +B+ -1 ]||l|l, |l| m a|||[|l|||l|||l COUPLING COUPLING 24 HO 24 HOLE MAGNETIC MAGNETIC I fin I FIELD w-21% 125 I ELECTRON OLLECTOR ELEG'I'RO OLLECTOR GUN GUN FIG. 3 FIG. 4

INVENTORS FREDERICK KARL WILLENBROCK STUART P. COOKE ATTOR N EY Patented Apr. 27, 1954 MODULATOR FOR MICROWAVE OSCILLATIONS Frederick Karl Willenbrock and Stuart P. Cooke, Cambridge, Mass., assignors to the United States of America as represented by the Secretary of the Navy Application October 20, 1950, Serial No. 191,116

19 Claims.

I This invention relates to microwave apparatus and more particularly to an electron tube adapted for use in a microwave system for modulating a microwave signal.

Heretofore modulation of a microwave energy could not be accomplished without the internal modification of a microwave generator itself. An

electron tube, known as the electron coupler,

described on pages 270 through 303 of the June, 1949, issue of the RCA Review, volume 10, No. 2, has been developed for the amplitude modulation of ultra-high frequencies but this tube has certain undesirable limitations. The tube therein described consists essentially of an electron gun, an input cavity which is connected to a source of ultra-high frequency power, an output cavity which is coupled to a load and a collector. The two cavities are positioned axially adjacent to each other and are tuned to the cyclotron frequency of a magnetic field which is oriented parallel to the axis of alignment of the two cavities. The cavities have the property, when excited, of introducing an alternating electric field normal to the magnetic field. The spiraling electron beam passes through both cavities absorbing the radio frequency power in the input cavity in the form of rotational energy and delivering this power to the output cavity and load or to the collector. The power transfer from the input cavity to the second cavity and the load may be controlled by varying either the beam current or the electron transit time in the output cavity. The electron coupler, because of the shape of the cavities used, is limited to use at ultra-high frequencies. The axial alignment of the cavities further presents a difficult problem of applying a uniform magnetic field through both cavities of sufiicient strength to maintain the spiraling beam at the cyclotron frequency.

The present invention is directed to apparatus for either amplitude-, phase-, or frequencymodulating signals having microwave frequencies of wavelengths from below 1 centimeter to approximately centimeters. The apparatus consists generally of a single cylindrical cavity resonator designed to oscillate in the TE111 mode to which is coupled the signal to be modulated, output coupling means disposed 90 in space from the input coupling, an electron gun arranged to project a beam of electrons axially through the cavity, and a collector. A beam of electrons is projected alon the axis of the resonator and under the influence of a steady magnetic field applied along the axis of the cavity assumes a. spiral path through the cavity. The spiraling electron beam passing through the cavity excites a second 'I'Emmode in the cavity which is displaced in Space from the mode excited from the external source. This second mode is coupled from the output coupling means to a utilization circuit, the degree of coupling being dependent upon the electron beam current or the beam voltage.

Accordingly, a primary object of the present invention is to provide means for modulating a microwave signal.

A further object of the present invention is to provide means for modulating a microwave signal by modulating the coupling of energy between the planes of polarization in a symmetrical resonator.

These and further objects will become apparent from the following detailed description when considered with the accompanying drawings in which:

Fig. 1 is a perspective view, partially in section, of a preferred embodiment of the present invention;

Fig. 2 is a sectional view taken transversely to the axis of the cavity resonator of Fig. 1 useful in explaining the operation of the invention;

Fig. 2A is a curve showing the instantaneous configuration of the electron beam within the cavity of Fig. 1 useful in explaining the operation of the invention;

Fig. 2B is a sketch useful in explaining the operation of the invention;

Figs. 3 and 4 are transverse cross sections of the cavity of Fig. 1 illustrating two methods of applying a modulating signal to the cavity; and

Fig. 5 is a graph illustrating the power coupling capabilities of the apparatus of the invention.

Referring to Fig. 1 there is illustrated a preferred embodiment of the invention comprising essentially a hollow cylindrical cavity resonator l G of conducting material having a pair of small openings II and i2 located on the axis of the cavity in the opposite end faces thereof. Microwave energy of suitable frequency is coupled to the resonator from a microwave generator l5 through suitable wave transmission means and then through an input coupling iris 18 formed in the wall of the resonator. A second iri displaced 90 in space from the input iris couples energy from the resonator for transmittal through suitable wave transmission means to a utilization-circuit l 6. An electron gun is of conventional design arranged coaxially with the cavity, projects a beam of electrons it through opening II, along the axis of the cavity through opening 12 in the opposite end of the cavity.

and thence to a collector M. For operation of the apparatus, means are necessary for producing a steady magnetic field axially of the cavity, but for reasons of simplicity no apparatus has been shown for producin this field, the existence of the field being indicated by properly legended arrows.

Having described generally the structure of the invention, the mode of operation thereof will now be discussed. It is well known in the art that a symmetrical cylindrical cavity dimensioned to oscillate in the TEm mode will oscillate when excited by a microwave signal of proper frequency coupled into the resonator. In the apparatus shown in Fig. 1 and in the schematic transverse section of Fig. 2, when power is coupled into the resonator through the iris l8, the resonator oscillates only in the mode indicated by the solid lines and no energy will be coupled out iris l1. electrons through the cavity, which is caused to follow a spiral trajectory under the influence of an axial magnetic field, indicated by the solid circle iii at the central portion of the sketch of Fig. 2, energy is coupled from the mode indicated by the solid lines to excite a second mode displaced 90 in space from the first mode as indicated by the dashed lines of Fig. 2. The degree of coupling between the exciting mode and the perpendicular mode depends on the accelerating voltage and the current of the electron beam projected through the cavity. Accordingly, modulation of the microwave signal may be obtained by varying either the beam current or the beam voltage. These variations are conventionally expressed in terms of Y0, which is beam admittance, defined as Io/Vo, where I0 is the beam current and V0 is the beam accelerating voltage.

The coupling between the two modes of oscillation, or planes of polarization, is'caused by the spiraling trajectory followed by the electron beam. The electrons transfer energy from the mode driven by the external microwave generator to the other mode located at right angles in space. Although individual electrons of the electron beam follow a spiral trajectory, a projection on a transverse plane of the cavity at any instant of a succession of electrons transversing the cavity would show a line of electrons each having the same azimuthal angle but with a greater radial deflection for the electrons which had been in the cavity for a longer interval of time. Accordingly, the beam of electrons is bunched in azimuthal angle so that all the electrons are effectively located in a single plane.

This plane rotates around the axis of symmetry of the cavity at a frequency We, which is equal to the resonant frequency of the cavity, This transverse projection, showing the radial deflection of the electron beam, is illustrated in Fig. 2A, the Z-axis being the axis of symmetry of the cavity, and the X-axis being at right angles thereto, the origin of the coordinate system being located at the point of entry of electrons into the cavity. The path which the lines shown in Fig. 2A follows in its rotation about the axis of symmetry of the resonator is illustrated by the solid line circle i9 in the sketch of Fig. 2.

The manner in which energy is coupled from the exciting mode to the mode at right angles thereto can be understood by a more detailed examination of Fig. 2. Remembering that the electron beam is made up of negative charges, for convenience the electric field vectors sketched therein are to be considered negative E vectors.

However, by projecting a beam of As the electron beam rotates in the direction indicated, the beam picks up energy while going down the E lines of the excited field (solid lines) and as the beam rotates further it gives up energy to the other mode as it comes into opposition with the E lines of the perpendicular field (dashed lines). Since the E fields in both modes reverse during each half revolution of the electron beam, the beam essentially picks up energy from the exciting mode during one-half of each revolution and gives up energy to the other mode during the other half of the revolution. Since the frequency of angular rotation of the electron beam equals the frequency of the radio frequency field, this process continues as the electrons traverse the cavity. Part of the energy in the second mode, because of the orientation thereof, is coupled out of the cavity through the second iris l! and applied to a utilization circuit.

By exciting the second mode of oscillation, the electron beam effectively rotates the plane of polarization of the cavity oscillation. Thus, by varying the current or the accelerating voltage of the electron beam, the amplitude of oscillation of the second plane of polarization of the cavity may be modulated. The resultant field of oscillation within the resonator is dependent on the relative magnitudes of the radio frequency field in the plane of polarization driven by the external generator and the amplitude of the radio frequency field in the perpendicular plane of polarization.

Referring to Fig. 2B, for a quiescent value of beam current and voltage selected to fall within the operative range of the system, let 51 be the angle determined by the amplitude of the two fields when Em is the amplitude of the exciting field and Em is the amplitude of the radio frequency field in the perpendicular plane of polarization (Y-axis plane). Then, as the beam current, Io, or accelerating voltage, V0, is varied from the aforementioned quiescent value, the plane of polarization angle of the resultant field is varied from the 51 value. Calling the instantaneous value of this deviation 5 and {30 the maximum deviation, and assuming that ,8 is varied according to the expression fi=fio sin wit, where h: wz/21.=the frequency of the modulating signal, the signal reflected back through the X-axis coupling iris, designated as E'ix will be proportional to cos c, and the signal seen through the Y-axis coupling iris, designated as Ec x, will be proportional to sin {3. Assuming further that E lx varies as cos wet where we is 211' times the resonant frequency of the cavity, E'fiyx will vary as -sin wet. Thus it follows that where in and k2 are proportionality constants and Just) represents the Bessel function of the first kind of order n.

To obtain an amplitude-modulated signal with a suppressed carrier, the signal from the Y-axis coupling iris is used with so chosen so that only the J 1( (3o) term is significant. If part of the original driving signal is combined with the signal represented by the Jiqeo) term, then an amplitude modulated signal with the carrier present is obtained. To obtain a phase modulated signal, the signals E'lx and E'z x should be combined without change of relative phase with A frequency modulated signal can be obtained by predistorting the original modulating signal by passing it through a conventional series RC circuit in a manner well known in the art. If an output is taken across the capacitor of the RC circuit, the modulation signal amplitude will vary inversely with the frequency. Thus, ,80 would be inversely proportional to the frequency as required for frequency modulation.

Referring to Figs. 3 and 4 there are illustrated two methods of applying a modulating signal to the cavity. In both figures, cavity I0 is shown in transverse section, the gun l3 projecting the electron beam 59 along the axis of the cavity towards the collector ltl mounted opposite the gun. A magnetic field oriented parallel to the axis of the cavity is provided by means not shown. A source of accelerating potential connected between the electron gun and the cavity accelerates the electron beam through the cavity and a second voltage source 22 connected between the cavity and the collector insures the removal of all electrons from the cavity. In Fig. 3, a source of modulating voltage is coupled in series with source 20 to modulate the accelerating potential V0 of the electron beam thereby to change the beam admittance.

As previously mentioned, the beam admittance may also be changed by varying the beam current. In the circuit shown in Fig. 4, the accelerating voltage is maintained at a constant value, a grid structure 2% is provided in the path of the electron between the electron gun and its point of entry into the cavity, and the source 24 of modulating voltage is connected between the electron gun It and the grid. Accordingly, the beam admittance is varied by varying the beam current, Io, in accordance with the modulating signal on the grid.

A representative tube built in accordance with the principles outlined above and designed to operate at 9000 megacycles was constructed of a copper resonator .790" long and 1% in diameter. The magnetic field necessary to produce cyclotron frequency for this size of cavity was .32 Weber per square meter (3,200 gauss) and a practical range for the beam admittance Yo was from 10* to 10- mhcs.

Qperating the apparatus constructed as hereinabove described and excited with representative values of voltage and current, data were obtained which were in substantial agreement with the theoretical plot of Fig. 5, which shows the power coupled to the driven plane of polarization as a function of the beam admittance. The curve can also represent the ratio of the power coupled out of the cavity to the utilization circuit to the power coupled into the resonator from the microwave generator. It will be observed that for values or beam admittance in the range between l0 to 10 mhos, there is little change in the ratio of coupled power with changes in beam admittance. Therefore, in using the apparatus as a modulator, it is desirable to select a quiescent point on the steep portion of the curve so that variations in the beam admittance by variation in the beam voltage V0 (Fig. 3), or by variation in the beam current (Fig. 4) will perceptivelymodulate the output power. Since the presence of the electron beam within the cavity has a small effect on the cavity, the admittance to the cavity is essentially constant thereby permitting modulation within the cavity without a shift of the generator frequency. Accordingly, the microwave generator of Fig. 1 may be any conventional microwave generator.

Referring again to Fig. l, the cavity is shown as being completely hollow with the electron beam passing axially thereof. This arrangement requires a vacuum seal on the coupling irises as well as between the electron gun around the opening II and the collector is to the opening l2. The irises are sealed with a window material transparent to microwave energy whereby energy is coupled to the respective wave guides associated therewith in a conventional manner. To re duce the problem of maintaining a vacuum in such a large volume, the tube may be modified by enclosing the region surrounding the electron beam in a glass tube extending centrally of the cavity and sealing only this to the electron gun and the collector. This alternate construction makes it unnecessary to maintain a vacuum in the entire cavity and also permits the use of coupling loops for exciting and extracting energy from the cavity. As a further modification the collector is could be located within the cavity itself. Further, the foregoing discussion has been confined to a resonator or circular cross-section. but the invention i equally applicable to resonators having transverse sections of other shapes, for example, a square cross-section, the only requirement being that the cavity be symmetrical and capable of sustaining oscillations therein in two modes in quadrature planes of polarization. Thus, while there is shown a particular embodiment of the invention, it will of course be under stood that it is not limited thereto since various modifications can be made and it is contemplated by the appended claims to cover any such modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. Microwave apparatus comprising means for establishing a microwave oscillating electromagnetic field, means for directing a beam of electrons axially through said field, means for imparting a spiralling movement to said beam at a frequency equal to the frequency or" said field, means for modulating said beam, said beam directing and modulating means being constructed and arranged to orient said modulated beam in said field so as to transfer energy from one mode of oscillation of said field to another mode of oscillation and means for extracting energy from said latter mode of oscillation.

2. Microwave apparatus comprising means for establishing a microwave electromagnetic field oscillating in a first plane of polarization, means for directing a beam of electrons through said first field, means for imparting a spiralling movement to said beam at a frequency equal to the frequency of said field, means for modulating said beam, said beam directing and modulating means being constructed and arranged to orient said modulated beam in said first field so as to couple energy from said first plane of polarization to excite oscillations having a second plane of pola -ization angularly displaced in space from said first plane of polarization and means for extracting energy from said second plane of polarization.

3. Microwave apparatus comprising a symmetrical resonator capable of sustaining oscillations in quadrature planes of polarization, means for exciting a microwave electromagnetic field in a first of said planes of polarization, means for directing a beam of electrons through said first field, means for imparting a spiralling movement to said beam at a frequency equal to the resonant frequency of said resonator, means for modulating said beam, said beam directing and modulating means being constructed and arranged to orient said modulated beam in said first field to couple energy from said first plane of polarization to excite oscillations in the other of said planes of polarization and output means associated with said other plane of polarization.

4. Microwave apparatus comprising a symmetrical resonator capable of sustaining oscillations therein in quadrature planes of polariza tion, means for exciting a microwave oscillating field in one of said planes of polarization, means for directing a beam of electrons axially through said field, means for imparting a spiraling movement to said electron beam at a frequency equal to the resonant frequency of said resonator whereby oscillations are excited in the other plane of polarization and means for coupling energy from said other plane of polarization to a utilization circuit.

5. Microwave apparatus comprising a symmetrical resonator adapted to sustain oscillations therein in two modes angularly displaced from each other, means for establishing microwave oscillations in one of said modes, means for directing a beam of electrons axially through said resonator, means for imparting a spiraling movement to said electron beam at a frequency equal to the resonant frequency of said resonator whereby said beam transfers energy from the established mode to a second mode angularly displaced thereirom, means for modulating said electron beam and means for extracting energy from said second mode.

6. Microwave apparatus comprising a symmetrical resonator adapted to sustain oscillations I in two angularly displaced planes of polarization, means for exciting a first microwave oscillating field in one or said planes of polarization, means for directing a beam of electrons through said first field, means for imparting a spiraling movement to said electron beam at a frequency equal to the resonant frequency of said resonator, means for modulating said electron beam prior to its passage through said first field, said beam directing and modulating means being arranged to orient said beam within said resonator so as to couple energy from said first field to excite oscillations in the other of said planes of polarization, and means for coupling energy from said other plane of polarization.

'7. Microwave apparatus comprising a cylindrical cavity resonator, means for establishing a microwave electromagnetic field within said cavity oscillating in a first plane of polarization, means for directing a beam of electrons along the axis of said cavity through said field, means for imparting a spiralling movement to said beam at a frequency equal to the resonant frequency of said resonator, means for modulating said beam prior to its passage through said field, said beam directing and modulating means being arranged to orient said beam so as to transfer energy from said first plane of polarization to excite oscillations in a second plane of polarization angularly displaced in space from said first plane of polarization, the angular orientation of the resultant field of said fields in said first and second planes of polarization being modulated in accordance with the modulation of said beam and means for removing energy from said second plane of polarization.

8. Microwave apparatus comprising a symmetrical resonator adapted to sustain oscillations in two angularly displaced planes of polarization, first and second coupling means similarly angularly displaced associated with said resonator, a microwave generator coupled to said first coupling means for exciting a first microwave oscillating field in a first of said planes of polarization, means for directing a beam of electrons through said first field, means for imparting a spiral movement to said beam at a frequency equal to the resonant frequency of said resonator, and means for modulating said beam, said beam directing and modulating means being arranged to orient said beam so as to couple energy from said first field to excite oscillations in the second of said planes of polarization, the angular displacement of the resultant field of said first and second fields being modulated in accordance with the modulation of said electron beam, said second coupling means being arranged to couple energy from said second field.

9. Microwave apparatus comprising a cylindrical resonator adapted to sustain oscillations in the TEm mode in quadrature planes of polarization, a microwave generator coupled to said resonator for coupling energy thereto to excite a first electromagnetic field in one of said planes of polarization, means for directing a beam of electrons axially through said resonator, means for imparting a spiral movement to said beam at an angular frequency equal to the resonant frequency of said resonator, means for modulating said electron seam, said beam directing and modulating means being arranged to orient said beam so as to couple energy from said first field to excite a second electromagnetic field in the other of said planes of polarization, said first and second fields producing a, resultant field the angular displacement of wl'iich is modulated in accordance with the modulation of said electron beam, and means for coupling energy from said second field of oscillations.

10. In combination, a cylindrical resonator having small apertures centrally located in the end walls thereof, means disposed at one end of said resonator for projecting a beam of electrons axially through said resonator through said apertures, a microwave generator coupled to the cylindrical wall of said resonator for exciting a first oscillating electromagnetic field in a first plane of polarization within said resonator, means for establishing a magnetic field axially of said resonator of sufficient intensity to impart spiral movement to said electron beam at a frequency equal to the resonant frequency of Said resonator, and means positioned from said first-mentioned coupling means for coupling energy from said resonator, said electron beam being eficctive to couple energy from said first to excite a second field in a plane spaced 90 from said first plane, said first and second fields producing a resultant field the angular displacement of which is modulated in a cordance with the modulation of said electron beam.

11. In combination, a cylindrical resonator having small apertures centrally located in the end walls thereof and being adapted to sustain oscillations in quadrature planes of polarization,

means for initiating a first stationary electromagnetic field in one of said planes of polarization, means for projecting a beam of electrons axially through said resonator and through said apertures, means for imparting a spiralling movement to said electrons as they pass through said resonator of such a frequency that energy from said first field is contributed to said electron beam during one half of each revolution of the beam and given up during the other half of each revolution of the beam to excite a second stationary electromagnetic field in said second plane of polarization, means for modulating said electron beam to control the amplitude of oscillations in said second field, and means for coupling energy from said second field of oscillations.

12. Apparatus for modulating a microwave signal comprising, a symmetrical resonator adapted to sustain oscillations in quadrature planes of polarization, means for coupling said microwave signal into said resonator to maintain a stationary electromagnetic field in said first plane of polarization, means for projecting a beam of electrons axially through said first field, means for imparting a spiralling movement to said electrons of a frequency equal to the resonant frequency of said resonator whereby energy is transferred from said first field by said beam to excite a second stationary electromagnetic field in said second plane of polarization, means for modulating said beam of electrons to control the amplitude, of oscillations in said second field and means for coupling energy from said second field of oscillations.

13. Apparatus for modulating a microwave signal comprising, a symmetrical resonator adapted to sustain oscillations in quadrature planes of polarization, means for couplin said microwave signal into said resonator to maintain a stationary electromagnetic field in said first plane of polarization, means for projecting a beam of electrons axially through said first field, means for imparting a spiralling movement to said electrons of a frequency equal to the resonant frequency of said resonator whereby energy is transferred from said first field by said beam to excite a second stationary electromagnetic field in said second plane of polarization, means for modulating said beam of electrons to control the amplitude of oscillations in said second field, and means connected to said resonator and arranged to couple energy from said second field of oscillations.

14. In combination, means for setting up a first stationary field of electromagnetic oscillations having substantially parallel electric lines of force in the central region thereof, means for projecting a beam of electrons axially through said central region of said field in a direction substantially perpendicular to said electric lines of force, means for imparting a spiralling movement to said electrons as they pass through said field of a frequency equal to the frequency of said oscillations whereby said electron beam transfers energy from said first field and excites a second stationary field displaced 90 in space from said first field and means for extracting energy from said second field.

15. In combination, means for setting up a first stationary field of electromagnetic oscillations having substantially parallel electric lines of force in the central region thereof, means for projecting a beam of electrons axially through said central region of said field in a direction substantially perpendicular to said electric lines of force, means for imparting a spiralling movement to said electrons as they pass through said field of a frequency equal to the frequency of said oscillations whereby said electron beam transfers energy from said first field and excites a second stationary field displaced in space from said first field, means for modulating said beam of electrons to similarly modulate the amplitude of oscillations in said second field and means for coupling energy from said second field of oscillations.

16. In combination, means for setting up a first stationary field of electromagnetic oscillations having substantially parallel electric lines of force in the central region thereof, means for projecting a beam of electrons axially through said central region of said field in a direction substantially perpendicular to said electric lines of force, means for imparting a spiralling movement to said electrons as they pass through said field of a frequency equal to the frequency of said oscillations whereby said electron beam transfers energy from said first field and excites a second stationary field displaced 90 in space from said first field, means for modulating said beam of electrons to similarly modulate the amplitude of oscillations in said second field, and means for coupling energy from said second field.

17. In combination, a symmetrical cylindrical resonator having small apertures centrally located in the end walls thereof, a generator coupled to said resonator for maintaining a first stationary field of electromagnetic oscillations within said resonator, means disposed externally of said resonator for projecting a beam of electrons through said apertures axially of said resonator, means for establishing a magnetic field axially of said resonator of a value to cause said electrons to follow a spiral trajectory at the frequency of said oscillations whereby energy is transferred by said beam from said first field to excite a second stationary field of oscillations displaced 90 from said first field and output means associated with said second stationary field of oscillations.

18. In combination, a symmetrical cylindrical resonator having small apertures centrally located in the end walls th reof, a generator coupled to said resonator for maintaining a first stationary field of electromagnetic oscillations within said resonator, means disposed externally of said resonator for projecting a beam of electrons through said apertures axially of said resonator, means for establishing a magnetic field axially of said resonator of a value to cause said electrons to follow a spiral trajectory at the frequency of said oscillations whereby energy is transferred by said beam from said first field to excite a second stationary field of oscillations displaced 90 from said first field, means for modulating said electron beam to control the amount of energy transferred from said first field to said second field and output means associated with said second field for deriving modulated energy therefrom.

19. In combination, a symmetrical cylindrical resonator having small apertures centrally located in the end walls thereof, a generator coupled to said resonator for maintaining a first stationary field of electromagnetic oscillations within said resonator, means disposed externally of said resonator for projecting a beam of electrons through said apertures axially of said resonator, means for establishing a magnetic field axially of said resonator of a value to cause said electrons to follow a spiral trajectory at the frequency of said oscillations whereby energy is References C e in the fi 01 this Pat transferred by said beam from said first field to UNITED STATES PATENTS excite a second stationary field of oscillations N b r N D te displaced 90 from said first field, means for mod- 23 3 Sh 3: Oct 1946 ulating said electron beam to control the amount 3, g z ga- Jail 1950 of energy transferred from said first field to said 2580970 stickler Jan. 1 1952 second field, and a utilization circuit coupled to said resonator 90 in space from said generator for deriving modulated energy from said second field. 10 

